Piezoelectric actuatable valve

ABSTRACT

In the case of a piezoelectrically operable valve ( 1 ) with at least one valve channel ( 4, 5 ), which can be closed by means of a sealing element ( 14, 16 ) held on a piezoelectric bending transducer ( 7, 8 ), the bending transducer ( 7, 8 ) is held at both ends in the valve housing ( 2 ) to increase the sealing effect of the closed valve channel or valve channel to be closed ( 4, 5 ). In this case, a first end ( 7   a,    8   a ) of the bending transducer ( 7, 8 ) is fixed in the valve housing ( 2 ), while the second end ( 7   b,    8   b ) is guided movably in the longitudinal direction ( 12 ) of the transducer in a housing groove ( 11 ) on the opposite housing side ( 2   b ).

[0001] The invention relates to a piezoelectrically operable valve withat least one valve channel, which can be closed by means of a sealingelement held on a piezoelectric bending transducer.

[0002] DE 36 08 550 A1 discloses a piezoelectrically operable valve,into the valve housing of which at least three valve channels open outto form a three-way valve. The valve, which can be used as a pneumaticvalve or hydraulic valve, has within its valve housing at least onepiezoelectric bending transducer, the connecting end of which, forconnecting an electric voltage source, is fixed in a narrow side of thehousing. The free end of the bending transducer, protruding into theinterior space of the housing, carries on its side facing the respectivevalve channel a sealing element for closing this valve channel.

[0003] In order, in an initial state or state of rest with an outflowchannel open, to close an inflow channel lying opposite said outflowchannel, the corresponding bending transducer is mechanicallyprestressed and/or pressed against the valve seat of the inflow channelby means of spring force. In this state, the opposite outflow channel isopened by a sealing element which is held by the same or a furtherbending transducer, that is fixed in the housing on the connection side,being situated opposite the valve seat of the outflow channel at adistance from it.

[0004] In the operating state, the connecting end of the bendingtransducer or of each bending transducer is connected to a voltagesource, the free end of the bending transducer being deflected in thedirection of the respective valve channel or in the opposite direction,depending on the polarity. As a result, the sealing element moved alongwith the free end of the bending transducer closes the outflow channelwhile the inflow channel is at the same time opened. As a result, amedium flowing into the valve housing via the inflow channel is carriedaway via a working channel, whereas in the state of rest, with theinflow channel closed, a medium flowing in via the working channel flowsout of the valve housing via the outflow channel.

[0005] In the case of this known piezoelectrically operated valve thereis the problem, in particular under extreme operating conditions, ofinadequate tightness of the valve channel closed according to theoperating state. Consequently, when a medium is passed via the valve ata high pressure and/or high flow rate, undesirably high leakage ratesmay occur as a result of inadequate sealing, in particular of the valvechannel that is open in the state of rest and is to be closed by meansof the excited bending transducer.

[0006] A piezoelectrically operated valve known from U.S. Pat. No.5,630,440 has a bending transducer that is clamped in the housing atboth ends and is consequently fixed by both its ends. As a result, acomparatively high restoring force or working force is admittedlyachieved in comparison with fixing of just one end of the bendingtransducer. However, the fixing of the bending transducer at both endshas the considerable disadvantage of an only small, and thereforegenerally inadequate, deflection displacement or bending excursion.

[0007] The invention is therefore based on the object of specifying apiezoelectric valve, in particular a pneumatic valve, in which the valvechannel to be blocked is reliably closed, while the disadvantagesmentioned are avoided.

[0008] This object is achieved according to the invention by thefeatures of claim 1. For this purpose, the second end of the bendingtransducer, lying opposite the fixed first end, is guided in alongitudinal groove provided in the valve housing. This guidance, andthe mobility of the bending transducer in the excited state achieved asa result, permits a longitudinal movement of the bending transducer,while a lateral movement of the free end is prevented by the groove sidewalls forming stops on both sides for the free end when the bendingtransducer is excited.

[0009] In this case, the fixed end is expediently configured as aconnecting end which can be connected to an electric voltage source forvalve operation.

[0010] The invention is in this respect based on the idea that areliable closing of the valve channel to be blocked, and consequentlydeactivated in each case, can be achieved even under extreme operatingconditions, in particular in the case of a high pressure and a high flowrate of a medium flow to be controlled, by increasing the force, with atthe same time a deflection displacement or bending excursion that is asgreat as possible. This increased pressing force with which the sealingelement is pressed against the valve seat of the corresponding valvechannel by means of the respective bending transducer can be produced bythe bending transducer itself, with at the same time an adequatedeflection displacement, if said bending transducer is held at both endswithin the valve housing and at the same time is fixed only at one end,while the other end is merely supported in the manner of an abutment. Asa result, an improvement in the operating behavior of the bendingtransducer and an increase overall in the operating reliability of thevalve are achieved.

[0011] The invention is based here on the finding that, with the givenconnected voltage or operating voltage and accordingly with a constantbending moment of the piezoelectric transducer, the force produced bythe latter increases with a decreasing lever arm. If the bendingtransducer is consequently held at both ends, the pressing force exertedby the sealing element on the valve seat of the corresponding valvechannel as a result of a bending deflection of the bending transducer isdistinctly greater in comparison with a bending transducer that isclamped at one end and freely movable at the free end. If in this caseone of the ends of the bending transducer is guided in an axiallymovable manner, the deflection displacement is at the same time greaterthan in the case of a bending transducer fixed at both ends. Therefore,it is expedient to arrange the sealing element in the central region ofthe bending transducer, preferably with at least approximately the samedistance both from the fixed end and from the movably guided end.

[0012] In order to achieve reliable closing of a valve channel alreadywhen it is in the initial state or state of rest in a particular simpleand effective way, in an advantageous development the bending transduceris concavely bent in the direction of this valve channel in thede-energized state. The bending profile of the bending transducer in thede-energized or excitation-free state of rest is expediently achieved bythe bending transducer itself being prestressed in the manner of a leafspring. Such prestressing is in turn expediently achieved by a suitableproduction process. In this respect, a laminated bending transducer witha layer structure having at least one electrically conductive backinglayer and a piezoceramic layer is taken as a basis and, by heating andsubsequent cooling, leads to layers prestressed to varying degrees(prestressed layers) as a result of material-dependently differentcontraction properties. The different prestressing of the layers in turnleads to a bending deflection of the flat bending transducer about abending axis running transversely with respect to its longitudinal sidesand lying parallel to its narrow sides.

[0013] In a particularly preferred embodiment, two bending transducersare arranged running essentially parallel to each other within the valvehousing. Their respective connecting end, which can be connected to anelectric voltage source, for valve operation is in turn expediently theend that is held fixedly on the housing, while the respective free endis in turn held movably in the longitudinal direction. With respect to acentral axis of the housing, the two bending transducers are convexlycurved in the direction of the valve channel respectively assigned tothem. In the de-energized state, a first valve channel is in this caseclosed by means of a sealing element, carried by a first bendingtransducer, while an opposite second valve channel is open. Lyingopposite this second valve channel, at a distance from it, there is thena sealing element carried by the second bending transducer.

[0014] By applying the operating voltage with appropriate polarity, bothbending transducers are excited, so that the first valve channel isopened and the second valve channel is closed. A medium flowing into thevalve housing via an additional inflow channel is consequently led outof the valve housing via the second channel in the state of rest and viathe first channel in the operating state. Depending on the mode ofoperation, a medium flowing in via the open second valve channel canflow away out of the valve housing via the inflow channel.

[0015] When a single bending transducer is used, in the de-energizedstate it is concavely bent in the direction of a first valve channel, asecond valve channel, lying opposite said first valve channel, extendingwithin the valve housing to within the effective proximity of theconcave side of the bending transducer. In particular in this embodimentwith only a single bending transducer, the latter carries a sealingelement that is effective on both sides of its central region.

[0016] Exemplary embodiments of the invention are explained in moredetail below with reference to a drawing, in which:

[0017]FIG. 1 shows in a sectional representation a first configurationalvariant of a piezo-electrically operable valve with two bendingtransducers held at both ends,

[0018]FIG. 2 shows a second configurational variant of the valveaccording to FIG. 1,

[0019]FIG. 3 shows in a representation according to FIGS. 1 and 2 apiezoelectrically operable valve with a single bending transducer thatis held at both ends, and

[0020]FIG. 4 shows in representations A and B trial constructions of apiezoelectric bending transducer held at one end and at both ends in theexcited state and excitation-free state.

[0021] The same parts are provided with the same reference numerals inall the figures here.

[0022] The piezoelectrically operable valve 1 according to FIGS. 1 and 2has a valve housing 2, which preferably consists of plastic and iscuboidal, with a likewise cuboidal or else circular-cylindrical interiorspace 3. Two diametrically opposed valve channels 4 and 5 open out intothe interior space 3. A further valve channel or inlet channel 6,opening out into the interior space 3 of the valve housing 2, runstransversely with respect to the two valve channels 4 and 5. Arranged inthe interior space 3 of the valve housing 2 are two platelet-shapedbending transducers 7 and 8. Each bending transducer 7, 8 has aconnecting end 7 a, 8 a and a free end 7 b, 8 b. The respectiveconnecting end 7 a, 8 a of the bending transducer 7 and 8, respectively,is held in the region of a narrow side 2 a of the valve housing 2 on theconnection side and is fixed there. Connecting contacts 9, which areconnected to a respective voltage source U₁ and U₂ via connecting lines10, are led to the respective connecting end 7 a, 8 a of the bendingtransducer 7 and 8, respectively. The voltage sources supply a DCvoltage of, for example, 200 V.

[0023] On the opposite narrow side 2 b of the housing of the valve 1,the free ends 7 b, 8 b of the respective bending transducer 7 and 8,respectively, lie in housing grooves 11. Within these housing grooves11, the free ends 7 b, 8 b of the bending transducers 7 and 8 are heldmovably in the longitudinal direction 12 of the transducer, which alsocorresponds to the longitudinal direction of the housing. The housinggrooves 11 in this case form lateral stops for the respective free end 7b, 8 b, in or counter to the transverse direction of the housingillustrated by the arrow 13.

[0024] In the state of rest or initial state represented in theexemplary embodiment, the bending transducers 7, 8 are de-energized andconsequently excitation-free. In this state of rest, the right-handvalve channel 4 in the exemplary embodiment according to FIGS. 1 and 2is closed. For this purpose, the bending transducer 7 carries in thecentral region of the outer side facing this valve channel 4 a sealingelement 14, preferably consisting of plastic or rubber. This sealingelement bears against the valve seat 15 of the valve channel 4 and sealsthe latter off on the inner side of the housing. The pressing force F₁required for this purpose is applied by the bending transducer 7 itself,in that, in the state of rest, the latter is concavely curved in thedirection of the valve seat 15 and thereby prestressed in the manner ofa leaf spring by being fitted in a corresponding position.

[0025] The bending and curving profile represented of the respectivebending transducer 7, 8 is achieved by a special production process, inwhich a layer structure with an electrically conductive backing layer,preferably in the form of a flat sheet-metal strip, and with apiezoceramic layer adhesively held on it is prestressed in a way notrepresented in any more detail by heating and subsequent cooling alongthe longitudinal direction 12 of the transducer.

[0026] The bending transducer 8 assigned to the (left-hand) valvechannel 5, which transducer corresponds with respect to its shape andstructure to the bending transducer 7, likewise carries a sealingelement 16 in its central region. In the open state of the valve channel5 represented, this sealing element is arranged at a distance a from thevalve seat 17 of said valve channel. In the de-energized state of rest,this bending transducer 8 is also convexly curved in the direction ofthe valve seat 17 and consequently in the direction of the valve channel5.

[0027] For operating the valve 1, the two bending transducers 7 and 8are excited with appropriate polarity of the voltage sources U₁ and U₂.When this happens, the two bending transducers 7, 8 move in thedirection or bending direction of the arrow 13, so that the sealingelement 14 carried by the bending transducer 7 is lifted off the valveseat 15 and consequently opens the valve channel 4, while the sealingelement 16 carried by the bending transducer 8 is pressed against thevalve seat 17 and consequently closes the valve channel 5. The free ends7 b and 8 b of the two bending transducers 7 and 8 can be displacedthereby in the longitudinal direction 12 on account of being securedwithin the housing grooves 11. In this arrangement, the free ends 7 band 8 b are extended into the housing grooves 11 to such a depth thatthey cannot come out of the housing grooves 11 when there is a bendingdeflection of the bending transducers 7, 8 in the excited state.

[0028] Whereas in the state of rest the prestressing of the bent bendingtransducer 7 has the effect that the sealing element 14 carried by thelatter is already pressed with an adequately high pressing force F₁against the valve seat 15, the pressing force F₂ required for closingthe valve channel 5, which is open in the state of rest, is achieved bythe securement of the bending transducer 8 at both ends in combinationwith the central arrangement of the sealing element 16. The reason forthis is an increase in force brought about by a particularly favorablelever arm effect with a constant bending moment.

[0029] During the operation of the pneumatic valve 1, configured in theexemplary embodiment as a three-way valve, air L flowing into the valvehousing 2 at a given pressure p and at a given flow rate v via the inletchannel 6 is carried away out of the valve housing 2 via the valvechannel 5, which is open in this de-energized state of rest. The inflowchannel 6 may in this case be led into the interior space 3 in the wayaccording to FIG. 1 through a longitudinal side of the valve housing 2at least approximately at the same height as the two diametricallyopposed valve channels 4 and 5. Alternatively, the inlet channel 6 maybe led into the interior space 3 in the way according to FIG. 2 throughthe narrow side 2 b of the valve housing 2, provided with the housinggrooves 11. In the case of this embodiment, the inlet channel 6expediently runs between the two housing grooves 11 and consequentlyopens out between the two bending transducers 7 and 8 into the interiorspace 3.

[0030] For switching over the valve 1, the two bending transducers 7 and8 are excited by applying an operating voltage U with appropriatepolarity of the voltage sources U₁ and U₂ and are deflected in the samedirection (bending direction) 13. As this happens, the valve channel 4,which is closed in the state of rest, is opened, while the valve channel5, which is open in the state of rest, is closed. The air L flowing intothe valve housing 2 via the inlet channel 6, is consequently carriedaway via the valve channel 4. Appropriate polarity of the voltagesources U₁ and U₂ also allows both valve channels 4 and 5 to be openedor closed.

[0031] In the case of the variant represented in FIG. 3 without voltageconnections 9, 10, with a single bending transducer 7, which in turn isheld at both ends in the valve housing 2, in the exemplary embodimentthe central region of said transducer is curved or bent in the directionof the valve channel 4 in the state of rest. The valve channel 5 lyingopposite the valve channel 4 is lengthened in the interior space 3 inthe direction toward the sealing element 14′ and consequently extends towithin the effective proximity of the bending transducer 7. The sealingelement 14′ which is placed on or applied to the bending transducer 7and is effective both on the convex side and on the concave side of thelatter is expediently configured in such a way that it is curved on bothsides. Sealing curvatures 14′a, 14′b directed counter to each other arein this case expediently of a hemispherical design. As a result, aparticularly reliable sealing effect is achieved even with acomparatively small clear width or a comparatively small inside diameterof the valve channels 4, 5.

[0032] During the operation of the pneumatic valve 1 according to FIG.3, in the de-energized state—or else with appropriate polarity of thevoltage U (not represented)—the sealing element 14′ is pressed againstthe valve seat 15, and consequently the valve channel 4 is closed, whilethe valve channel 5 is open, by means of the pre-stressed, bent bendingtransducer 7. By polarity reversal of the voltage U, the valve channel 5is closed, and at the same time the valve channel 4 is opened, as aresult of a bending deflection of the bending transducer 7 counter tothe bending direction 13 represented.

[0033]FIG. 4 illustrates trial structures A and B with a single bendingtransducer 7 restrained on the connection side, the following statementsapplying analogously to the bending transducer 8 according to FIGS. 1and 2. Whereas according to trial A the free end 7 b of the bendingtransducer 7 is freely movable in the manner of a boom, according totrial B its free end 7 b is held such that it is merely longitudinallydisplaceable. In both trials A and B the same bending transducer 7 wasused, the piezoceramic layer of which had the dimensions38.00×12.70×0.20 and the backing layer of which had the dimensions63.4×13.7×0.15 (length, width and thickness in mm). Measuring parameterswere the required restoring force F to return the bending transducer 7excited with a voltage U=200 V (DC) at the respective point P_(A), P_(B)from the deflected position A_(a), B_(a) into the excitation-free restor neutral position A_(b) or B_(b), respectively.

[0034] In trial A, the restoring force F was registered at the free end7 b of the bending transducer at the measuring point P_(A), while intrial B this was determined in the central region of the bendingtransducer 7 at the measuring point P_(B). The restoring force Fcorresponding to the pressing force F_(1,2) was measured in trial A at0.2 N (corresponds to 20 g) and in trial B at 1.25 N (corresponds to 125g).

[0035] This means that the arrangement according to the invention of abending transducer 7, 8 held at both ends, with a sealing element 14, 16arranged in its central region, within a piezoelectrically operatedvalve 1 achieves an increase many times over of the force F_(1,2) forclosing a valve channel 4 or 5 in comparison with a piezo elementrestrained at one end.

1. A piezoelectrically operable valve (1) with at least one valvechannel (4, 5), which can be closed by means of a sealing element (14,16) held on a piezoelectric bending transducer (7, 8), in whicharrangement the bending transducer (7, 8), having a first end (7 a, 8 a)and a second end (7 b, 8 b), is fixed by the first end (7 a, 8 a) in thevalve housing (2), and the second end (7 b, 8 b) of the bendingtransducer (7, 8) is guided movably in the longitudinal direction (12)of the transducer in a housing groove (11) on the housing side (2 b)lying opposite the first end (7 a, 8 a).
 2. The piezoelectricallyoperable valve as claimed in claim 1 , characterized in that the firstend (7 a, 8 a), fixed in the valve housing (2), is configured as aconnecting end of the bending transducer (7, 8) which can be connectedto an electric voltage source (U_(1,2)) for valve operation.
 3. Thepiezoelectrically operable valve as claimed in claim 1 or 2 ,characterized in that the bending transducer (7, 8) is concavely bent inthe direction of the valve channel (4, 5) in the de-energized state. 4.The piezoelectrically operable valve as claimed in one of claims 1 to 3, characterized in that the sealing element (14, 16) is arranged in thecentral region of the bending transducer (7, 8).
 5. Thepiezoelectrically operable valve as claimed in one of claims 1 to 4 ,characterized in that, in the de-energized state, a first valve channel(4) is closed by means of a first sealing element (14), which is held ona first bending transducer concavely bent in the direction of this valvechannel (4), while a second valve channel (5), lying opposite the firstvalve channel (4), is open, said second valve channel having opposite itand at a distance from it a second sealing element (16), which is heldon a second bending transducer (8) concavely bent in the direction (13)of this valve channel (5).
 6. The piezoelectrically operable valve asclaimed in one of claims 1 to 5 , characterized by an inlet channel (6)opening out into the valve housing (2) transversely with respect to eachvalve channel (4, 5).
 7. The piezoelectrically operable valve as claimedin claim 1 , characterized in that, when a single bending transducer (7)is used, in the de-energized state it is concavely bent in the directionof a first valve channel (4) and convexly bent with respect to a secondvalve channel, lying opposite it, the second valve channel (5) extendingwithin the valve housing (2) to within the effective proximity of thebending transducer (7).
 8. The piezoelectrically operable valve asclaimed in claim 7 , characterized by a sealing element (14′) that iseffective on both sides of the central region of the bending transducer(7).
 9. The piezoelectrically operable valve as claimed in one of claims1 to 8 , characterized in that the sealing element (14′) has a sealingcurvature (14 a, 14 b) directed toward the respective valve channel (4,5).